1) Field of the Invention
This invention relates in general to novel silicon compounds. In one aspect, this invention is directed to tert-alkyl carbamate silicon compounds which when activated (i.e., deblocked) are particularly useful as coupling agents. In another aspect this invention is directed to tert-alkyl carbamate silicon compounds which are latent coupling agents and wherein the carbamate silicon compounds are compatible and stable in the presence of a variety of sizing and coating agents, such as antistats, lubricants, film formers and other chemicals employed in the protection of surfaces, particularly inorganic oxide surfaces, from abrasion and corrosion. The invention is also directed to processes for the preparation of novel silicon compounds, to processes for activation (deblocking) to aminosilane coupling agents, and to processes for their use in aqueous sizes for improving adhesion between resinous systems and inorganic oxide materials, particularly fiber glass.
2) Description of the Related Art
Organofunctional silane compounds have been employed in the treatment of a variety of surfaces, such as metal oxides, silicates, particulate siliceous fillers and pigments, and fibers such as glass fibers, steel fibers and aluminum fibers. (Metal surfaces are regarded as oxide surfaces because they are oxidized even though their subsurfaces are not). Some organofunctional silane treatments involve coating such a surface with an aqueous solution of the silicon compound either alone or in conjunction with other chemicals.
Other modes of treatment involve coating such surfaces with an organic or aqueous organic solution of the silicon compound either alone or in conjunction with other chemicals, or coating the surface with the silicon compound without the aid of a solvent. In some instances, the silicon compound can be added directly to the resinous media (integral blend).
As a rule, the treatment enhances bonding between the inorganic oxide surfaces and resinous media. Consequently, the silicon compounds have utility as components in primers in the application of coatings, adhesives or sealants to inorganic oxide surfaces and as a filler pretreatment to improve the strength and structural integrity of filled resin composites such as those incorporating fiber glass. Such organofunctional hydrolyzable silanes are termed "Coupling Agents" or "Adhesion Promoters".
In addition to the improvement of bonding, coupling agents have found other uses related to their ability to alter the surface characteristics of inorganic oxides, such as their ability to protect glass fibers from abrasion and impart lubricity to the glass which is important in handling and processing the glass fibers.
Prior to the present invention, it was known that 3-aminopropyltriethoxysilane and other aminosilanes were often used to treat glass fibers either as continuous strands or as woven cloth. However, a problem has been in existence for some time which detracts from the use of such silanes in the treatment of glass fibers. It has been noted that silane treated glass fibers age prematurely. The amine groups react with carbon dioxide of the air to form carbamic acids. These acids make the glass fibers stiff and difficult to handle especially in the woven form. In addition, oxygen in the air can slowly oxidize the amino functional group of the silane. The oxidation products of the amino functional group are often not reactive with the organic resins and the silane coupling agent loses its coupling efficiency. In many instances, fabrics and continuous strands comprised of fiber glass become discolored because of the oxidation of the amino functional silane and accordingly are of less value.
It has also been noted that aminosilane compounds when used as coupling agents are not always compatible with the other components in the coating, primer or size, such as size or coating materials used in the processing of glass fibers. As hereinafter indicated, glass fibers, for example, usually require the presence of other ingredients such as film formers, lubricants, antistats, and the like, in order to impart desirable characteristics to the glass fibers. The presence of aminoorganosilanes in formulations containing such ingredients may not provide a system which is stable for any length of time, especially if the other ingredients are pH sensitive emulsions, and/or contain functional groups that can react with amines, such as epoxies, carboxylates and the like. Accordingly, there is a need in such cases for aminosilanes which can remain latent when in contact with other sizing (processing) components prior to the application of these materials to the surface but can be activated when desired to serve their function as coupling agents.
Accordingly, one or more of the following objects will be achieved by the practice of the present invention. It is an object of this invention to provide certain novel silicon compounds which can be activated to function as coupling agents. Another object of the invention is to provide novel tertiary-alkyl carbamate silicon compounds which when deblocked are useful as aminosilane coupling agents. A futher object is to provide tert-alkyl carbamate silicon compounds which upon heating or in the presence of a catalyst, decompose to form unsaturated hydrocarbons, carbon dioxide and aminosilanes. Another object of this invention is to provide tert-alkyl carbamate silicon compounds in which the organofunctional groups are dormant and unreactive in the presence of a variety of additives and chemicals employed in priming of inorganic surfaces, sizing or finishing fibers, coatings of inorganic oxide surfaces or when compounded with resinous materials. Another object is to provide latent silicon compounds which do not affect the stability of systems containing sizing and/or coating agents, such as antistats, emulsifiers, and the like, but when activated, function as coupling agents. Another object is to provide processes for the preparation of the tert-alkyl carbamate silicon compounds. An object is to prepare the novel carbamates by the reaction of a tertiary alcohol and an isocyanatofunctional silane. Another object is to prepare the carbamates by the reaction of a tertiary alcohol with an alkenyl isocyanate followed by hydrosilation with an hydridosilane. A further object is to prepare novel carbamates by the reaction of a tert-alkyl phenyl carbonate or a di-tert-alkyl carbonate with an amino functional silane. Another object is to provide stable coatings for glass fibers which contain a latent silicon coupling agent, antistats, film formers, lubricants and the like. A still further object is to provide processes for activating the tert-alkyl silicon compound for the purpose of coupling resinous systems and inorganic oxide surfaces, silicates and the like. These and other objects will readily become apparent to those skilled in the art in the light of the teachings herein set forth.